Characterization of the density fluctuations in turbulent V-shaped premixed flames

✍ Scribed by M. Namazian; I.G. Shepherd; L. Talbot

• Publisher: Elsevier Science
• Year: 1986
• Tongue: English
• Weight: 546 KB
• Volume: 64
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(86)90147-1

✦ Synopsis

Rayleigh scattering has been used to measure simultaneously two-point density fluctuations in a range of turbulent premixed flames. V-shaped ethylene/air and methane/air flames stabilized on a 1 mm rod were studied at equivalence ratios of 0.6 and 0.8 with approach flow mean velocities of 5 m/s and 7 m/s and turbulent intensities of 5% and 8%. Measurements were performed at different locations downstream of the flame holder. To characterize the flames, the measured flame brush thickness and the rms of the density fluctuations are compared. Time and length scales and other statistical quantities associated with the density fluctuations are reported.

The Bray-Moss-Libby model of premlxed turbulent combustion has recently been extended to include such characteristics of the scalar field as time and length scales, autocorrelations, and power spectra. This model is based on the thin flame approximation and treats the time series of the density fluctuations as a "random telegraph signal." The single-point experimental results reported here compare very well with the predictions of the model.

A wrinkled laminar flame sheet model which describes the turbulent flame region in terms of the instantaneous flame-front position is used to characterize these flames. It is shown that the pdf of the instantaneous flame location in the flame brush has a Gaussian distribution. Nondimensionalizing the flame density profile by a turbulent flame thickness derived from the maximum density gradient, all the data may be collapsed onto a simple error function plot.